Storks are large, long-legged, long-necked wading birds with long, stout bills. They belong to the family Ciconiidae, and make up the order Ciconiiformes /sɪˈkoʊni.ɪfɔːrmiːz/. Ciconiiformes previously included a number of other families, such as herons and ibises, but those families have been moved to other orders.[2]
Storks dwell in many regions and tend to live in drier habitats than the closely related herons, spoonbills and ibises; they also lack the powder down that those groups use to clean off fish slime. Bill-clattering is an important mode of communication at the nest. Many species are migratory. Most storks eat frogs, fish, insects, earthworms, small birds and small mammals. There are 20 living species of storks in six genera.
Various terms are used to refer to groups of storks,[3] two frequently used ones being a muster of storks and a phalanx of storks.
Storks tend to use soaring, gliding flight, which conserves energy. Soaring requires thermal air currents. Ottomar Anschütz's famous 1884 album of photographs of storks inspired the design of Otto Lilienthal's experimental gliders of the late nineteenth century. Storks are heavy, with wide wingspans: the marabou stork, with a wingspan of 3.2 m (10 ft 6 in) and weight up to 8 kg (18 lb), joins the Andean condor in having the widest wingspan of all living land birds.
Their nests are often very large and may be used for many years. Some nests have been known to grow to over 2 metres (6 ft 7 in) in diameter and about 3 metres (9.8 ft) in depth. All storks were once thought to be monogamous, but this is only partially true. While storks are generally socially monogamous, some species exhibit regular extra-pair breeding.[4]
Popular conceptions of storks' fidelity, serial monogamy, and doting parental care contribute to their prominence in mythology and culture, especially in western folklore as the deliverers of newborn humans.[5]
All 20 stork species have been assessed by the IUCN and carry a confident Red List status. However, the assessment for several species were based on incorrect assumptions and a general absence of sound information on stork habits.[6]
The word "stork " was first used in its current sense by at least the 12th century in Middle English.[7] It is derived from the Old English word "storc", which itself comes from the hypothesised Proto-Germanic *stork and ultimately the Proto-Indo-European *sr̥ǵos.[7][8] The name refers to the rigid posture of storks, a meaning reflected in the related word stark, which is derived from the Old English "stearc".[9] Several species of storks are known by other common names. The jabiru is named after the Tupí-Guarani words meaning "that which has" and "swollen", referring to its thickset neck.[10] The marabou stork is named after the Arabic word for holy man, murābiṭ, due to the perceived holy nature of the species.[11] The adjutants are named after the military rank, referring to their stiff, military-like gait.[12]
A DNA study found that the families Ardeidae, Balaenicipitidae, Scopidae and the Threskiornithidae belong to the Pelecaniformes. This would make Ciconiidae the only group.[13][14]
Storks were distinct and possibly widespread by the Oligocene. Like most families of aquatic birds, storks seem to have arisen in the Palaeogene, maybe 40–50 million years ago (mya). For the fossil record of living genera, documented since the Middle Miocene (about 15 mya) at least in some cases, see the genus articles.
No species or subspecies of stork is known to have gone extinct in historic times. A systematic literature review uncovered nearly 1,000 papers on storks, but showed most stork species to lack scientific understanding suggesting that many species should be classified as Data Deficient on the IUCN Red List. A Ciconia bone found in a rock shelter on the island of Réunion was probably of a bird taken there as food by early settlers; no known account mentions the presence of storks on the Mascarene Islands.
The following phylogeny is recognized by the International Ornithological Congress, partially based on de Sousa et al (2023):[15][16]
The fossil genera Eociconia (Middle Eocene of China) and Ciconiopsis (Deseado Early Oligocene of Patagonia, Argentina) are often tentatively placed with this family. A "ciconiiform" fossil fragment from the Touro Passo Formation found at Arroio Touro Passo (Rio Grande do Sul, Brazil) might be of the living wood stork M. americana; it is at most of Late Pleistocene age, a few 10,000s of years.[22]
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Storks range in size from the marabou, which stands 152 cm (60 in) tall and can weigh 8.9 kg (19+1⁄2 lb), to the Abdim's stork, which is only 75 cm (30 in) high and weighs only 1.3 kg (2+3⁄4 lb). Their shape is superficially similar to the herons, with long legs and necks, but they are more heavy-set. There is some sexual dimorphism (differences between males and females) in size, with males being up to 15% bigger than females in some species (for example the saddle-billed stork), but almost no difference in appearance. The only difference is in the colour of the iris of the two species in the genus Ephippiorhynchus.[23]
The bills of storks are large to very large, and vary considerably between the genera. The shape of the bills is linked to the diet of the different species. The large bills of the Ciconia storks are the least specialized. Larger are the massive and slightly upturned bills of the Ephippiorhynchus and the jabiru. These have evolved to hunt for fish in shallow water. Larger still are the massive daggers of the two adjutants and marabou (Leptoptilos), which are used to feed on carrion and in defense against other scavengers, as well as for taking other prey.[23] The long, ibis-like downcurved bills of the Mycteria storks have sensitive tips that allow them to detect prey by touch (tactilocation) where cloudy conditions would not allow them to see it.[24] The most specialised bills of any storks are those of the two openbills (Anastomus), which as their name suggests, is open in the middle when their bill is closed. These bills have evolved to help openbills feed on their primary prey item, aquatic snails.[25]
Although it is sometimes reported that storks lack syrinxes and are mute,[26] they do have syrinxes,[27] and are capable of making some sounds, although they do not do so often.[23][28] The syrinxes of storks are "variably degenerate" however,[27] and the syringeal membranes of some species are found between tracheal rings or cartilage, an unusual arrangement shared with the ovenbirds.[29]
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Storks have a nearly cosmopolitan distribution, being absent from the poles, most of North America and large parts of Australia. The centres of stork diversity are in tropical Asia and sub-Saharan Africa, with eight and six breeding species respectively. Just three species are present in the New World: wood stork, maguari stork and jabiru, which is the tallest flying bird of the Americas. Two species, white and black stork, reach Europe and western temperate Asia, while one species, Oriental stork, reaches temperate areas of eastern Asia, and one species, black-necked stork, is found in Australasia.[23]
Storks are more diverse and common in the tropics, and the species that live in temperate climates for the most part migrate to avoid the worst of winter. They are fairly diverse in their habitat requirements. Some species, particularly the Mycteria "wood storks" and Anastomus openbills, are highly dependent on water and aquatic prey, but many other species are far less dependent on this habitat type, although they will frequently make use of it. Species like the marabou and Abdim's stork will frequently be found foraging in open grasslands of savannah. Preferred habitats include flooded grasslands, light woodland, marshes and paddyfields, wet meadows, river backwaters and ponds. Many species will select shallow pools, particularly when lakes or rivers are drying out, as they concentrate prey and make it harder for prey to escape, or when monsoonal rainfall increases water depth of larger waterbodies.[23][30] Some species like the woolly-necked storks and lesser adjutant storks have adapted to changing crops of tropical agricultural landscapes that e